Existing safety shutdown systems do not provide an economical and rugged actuator that provides a strong mechanical pulling action over a distance when power is removed from the actuator. This pulling action over a predetermined distance may close a valve of the safety shutdown system. Ruggedness is desired since the actuator is typically exposed to outside environmental conditions, and often to vehicle undercarriage road conditions. In addition, the pulling action must be capable of side loading up to 20 degrees off the line of the actuator shaft, since it is not always possible to route the actuating cables perfectly in line with the actuator shaft.
The pulling force and distance required is a function of the valve being closed. In the area of safety devices for the NH3 or propane industry, the desired pulling force is approximately 50 pounds over a distance of at least one inch. This is the force and stroke needed to reliably close the typical internal valve found on delivery trucks and storage containers commonly used in the industry.
The requirement that the force be applied upon removal of power to the actuator is common practice in safety systems, so that in the event of a non-planned power loss, the device will “fail safe” and perform the desired safety function. The requirement that the safety action be performed in the absence of electrical power means that the power to perform the action must be “stored” in some form and “released” in the absence of electrical power. A common means of storing the energy to be released in the absence of electrical power is with a compressed spring. The spring is typically compressed over some distance, and then held in that potential energy position by some means. Standard pull type solenoids such as the Syncro-Start 2300 series are not suitable for this task, even though they have the required holding power, because the solenoid shaft cannot be “pulled” into the latch position as is required for a device that will compress and then hold the spring compressed. The Syncro-Start 1700 push series solenoids are more suitable for the task because the shaft can be pulled through a distance to compress a spring and into engagement with the “holding” position of the solenoid. However, push style solenoids inherently do not have a high ratio of “push” to “holding” power, and are only marginally suitable as safety shutdown actuators in the NH3 and propane industry.
The disadvantages of the prior art are overcome by the present invention, and an economical and highly reliable remote shutdown system and method are hereinafter disclosed to close a manually operated tank product valve on a product delivery vehicle.